class_docstr: Base class for row group indexers.
docstr: Return list of column(s) reuired to build index.
docstr_tok: ["Return","list","of","column","(","s",")","reuired","to","build","index","."]
code: def column_names(self):
      """Return list of column(s) reuired to build index."""
      return None
  
file_path: petastorm/petastorm/etl/__init__.py
imports: import abc
  import six
label_desc: Use image node_id 3 for calling the RowGroupIndexerBase obj's underlying member method code with example usage: obj.column_names() and returns: None